feat(client): 登录历史下拉、macOS 兼容修复、UI 优化

- 替换 flutter_secure_storage 为 shared_preferences，解决 macOS Keychain 签名报错
- 登录页门店编号/用户名支持历史下拉（最多5条，LRU 淘汰），使用 Overlay + CompositedTransformFollower 实现浮层
- logout 仅删除 auth token，保留登录历史
- AppShell 时钟抽为独立 _ClockWidget，避免每秒 setState 导致 TabBarView 叠影
- ShellRoute 子路由改用 NoTransitionPage，消除切换页面时的过渡动画叠影
- 新增 auth_state_test、auth_repository_test、login_screen_test 共 14 个单元/Widget 测试

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

client/lib/core/auth/auth_state.dart

@@ -1,5 +1,5 @@
 import 'package:flutter_riverpod/flutter_riverpod.dart';
-import 'package:flutter_secure_storage/flutter_secure_storage.dart';
+import 'package:shared_preferences/shared_preferences.dart';
 
 const _kAccessToken = 'access_token';
 const _kRefreshToken = 'refresh_token';
@@ -37,49 +37,54 @@ class AuthState {
 }
 
 class AuthNotifier extends StateNotifier<AuthState> {
-  final FlutterSecureStorage _storage;
+  AuthNotifier() : super(const AuthState());
 
-  AuthNotifier(this._storage) : super(const AuthState());
-
-  /// Called at app startup to restore persisted session
+  /// Called at app startup to restore persisted session.
   Future<void> restore() async {
-    final accessToken = await _storage.read(key: _kAccessToken);
-    final refreshToken = await _storage.read(key: _kRefreshToken);
-    final username = await _storage.read(key: _kUsername);
-    final realName = await _storage.read(key: _kRealName);
-    final hotelNo = await _storage.read(key: _kHotelNo);
-    final hotelIdStr = await _storage.read(key: _kHotelId);
+    try {
+      final prefs = await SharedPreferences.getInstance();
+      final accessToken = prefs.getString(_kAccessToken);
+      final refreshToken = prefs.getString(_kRefreshToken);
+      final username = prefs.getString(_kUsername);
+      final realName = prefs.getString(_kRealName);
+      final hotelNo = prefs.getString(_kHotelNo);
+      final hotelIdStr = prefs.getString(_kHotelId);
 
-    if (accessToken != null && refreshToken != null && username != null) {
-      state = AuthState(
-        initialized: true,
-        user: AuthUser(
-          accessToken: accessToken,
-          refreshToken: refreshToken,
-          username: username,
-          realName: realName ?? username,
-          hotelNo: hotelNo ?? '',
-          hotelId: int.tryParse(hotelIdStr ?? '') ?? 0,
-        ),
-      );
-    } else {
-      state = const AuthState(initialized: true);
+      if (accessToken != null && refreshToken != null && username != null) {
+        state = AuthState(
+          initialized: true,
+          user: AuthUser(
+            accessToken: accessToken,
+            refreshToken: refreshToken,
+            username: username,
+            realName: realName ?? username,
+            hotelNo: hotelNo ?? '',
+            hotelId: int.tryParse(hotelIdStr ?? '') ?? 0,
+          ),
+        );
+        return;
+      }
+    } catch (_) {
+      // Storage unavailable — fall through to logged-out state
     }
+    state = const AuthState(initialized: true);
   }
 
   Future<void> login(AuthUser user) async {
-    await _storage.write(key: _kAccessToken, value: user.accessToken);
-    await _storage.write(key: _kRefreshToken, value: user.refreshToken);
-    await _storage.write(key: _kUsername, value: user.username);
-    await _storage.write(key: _kRealName, value: user.realName);
-    await _storage.write(key: _kHotelNo, value: user.hotelNo);
-    await _storage.write(key: _kHotelId, value: user.hotelId.toString());
+    final prefs = await SharedPreferences.getInstance();
+    await prefs.setString(_kAccessToken, user.accessToken);
+    await prefs.setString(_kRefreshToken, user.refreshToken);
+    await prefs.setString(_kUsername, user.username);
+    await prefs.setString(_kRealName, user.realName);
+    await prefs.setString(_kHotelNo, user.hotelNo);
+    await prefs.setString(_kHotelId, user.hotelId.toString());
     state = AuthState(initialized: true, user: user);
   }
 
   void updateAccessToken(String newToken) {
     if (state.user == null) return;
-    _storage.write(key: _kAccessToken, value: newToken);
+    SharedPreferences.getInstance()
+        .then((prefs) => prefs.setString(_kAccessToken, newToken));
     state = AuthState(
       initialized: true,
       user: AuthUser(
@@ -94,15 +99,17 @@ class AuthNotifier extends StateNotifier<AuthState> {
   }
 
   Future<void> logout() async {
-    await _storage.deleteAll();
+    final prefs = await SharedPreferences.getInstance();
+    await prefs.remove(_kAccessToken);
+    await prefs.remove(_kRefreshToken);
+    await prefs.remove(_kUsername);
+    await prefs.remove(_kRealName);
+    await prefs.remove(_kHotelNo);
+    await prefs.remove(_kHotelId);
     state = const AuthState(initialized: true);
   }
 }
 
-final _secureStorage = FlutterSecureStorage(
-  mOptions: MacOsOptions(groupId: 'com.jiu.client'),
-);
-
 final authStateProvider = StateNotifierProvider<AuthNotifier, AuthState>(
-  (ref) => AuthNotifier(_secureStorage),
+  (ref) => AuthNotifier(),
 );